High speed axial flow compressors



April 1964 v. T. FORSTER HIGH SPEED AXIAL FLOW COMPRESSORS- Filed Oct.19, 1961 United States Patent "ice 3,129,257 6 HIGH SPEED AXIAL FLOWCOMPRESSORS Vincent Trevor Forster, Rugby, England, assignor to TheEnglish Electric Company Limited, London, England, a British companyFiled Oct. 19, 1961, Ser. No. 146,182 1 Claim. (Cl. 230-120) The presentinvention relates to axial flow compressors and has the primary objectof increasing the swallowing capacity thereof which is often limited bythe Mach number of the flow which can be accepted by the first row ofrotor blades, or even by the following further two rows of blades. Ifthis Mach number is increased above a critical value, say 0.65 to 0.75depending on the type, setting and pitch of the blades, shock stallingresults because sonic velocities are reached locally on the convex sideof the blades with consequent breakdown of the flow.

If the Mach number is further increased, a limiting value is reachedwhen the blade is said to be choked.

By increasing this limiting Mach number the mass flow through a givensize of engine and its output could be increased correspondingly, or thesize of gas turbine engine incorporating an axial flow compressor couldbe reduced for the same output.

Attempts at solving this problem by reducing the thickness-chord ratioand by sharpening the nose of the blades have obviously reached theirlimits. The present invention makes a difierent approach to this problemby applying the so-called area rule established for the design oftransonic aircraft, according to which only the integrated cross-sectionarea at any transverse plane is decisive for shock stalling eifects andnot the distribution of this area.

According to the present invention the leading edges of one of the firstrows of rotor blades are lengthened in the radial direction of the rotorboth as compared with the trailing edges of the said rotor blades andwith the trailing edges of the immediately preceding stator blades, andrecesses flaring out adjacent the tip and root of the said lengthenedleading edge are provided in the stator and rotor respectively, so thatthe cross sectional area of the throat at the entries betweenconsecutive rotor blades of this row is increased.

In order that the invention may be clearly understood and readilycarried into eiiect an embodiment thereof will now be described by wayof example with reference to 3,129,876 Patented Apr. 21, 1964 theaccompanying drawing, which is a diagrammatic part cross section of thefirst stage of an axial flow compressor, showing one rotor blade and theimmediately preceding and subsequent stator blades only.

In the stator -1 of an axial flow compressor a first row 2 and a secondrow 5 of stator blades are mounted in the usual manner. On the rotor 4,which is rotatable about the axis OO, a first row of rotor blades 3 ismounted, for example by means of the usual serrated roots 6.

The leading edge 7 of the rotor blade 3 is extended in the radialdirection of the rotor *4 as compared both with the trailing edge 8thereof and with the length of the preceding row of stator blades 2.=Recesses flaring out at 9 and 10 adjacent the tip and root of the saidlengthened leading edge 7 are provided in the stator l1 and rotor 4,respectively, so that the cross sectional area of the throat at theentries between consecutive rotor blades of this row is increased. Inthis way the limiting Mach number for the blade can be increased.

What I claim as my invention and desire to secure by Letters Patent is:

A subsonic multi-stage axialdlow compressor compris ing a stator and arotor defining respectively outer and inner boundaries of an annular-1yconverging working fluid pasasge, a row of stator blades mounted in saidstator, rotor blades mounted in said rotor and downstream of said statorblades, each rotor blade having a root and a tip, said passage having adiverging portion forming recesses adjacent the root and tiprespectively of the leading edges of the rotor blades and being longerthan the radial dimension of the adjacent stator blade, whereby thecross-sectional area of the passage at the leading edge is greater inmagnitude than the cross-sectional area at the trailing edge of theadjacent stator blade.

References Cited in the file of this patent UNITED STATES PATENTS2,628,768 Kantrowitz Feb. 17, 1953 2,846,136 Zaba Aug. 5, 1958 FOREIGNPATENTS 996,967 France Sept. 5, 1951 226,168 Great Britain of 1926564,336 Great Britain Sept. 22, !1944 661,861 Great Britain Nov. 28,1951

